February 10

On a Celsius thermometer, the freezing point of water is 0°. On the same thermometer, the boiling point of water is 100°.

These two statements are straightforward scientific facts. Educational philosophers refer to the ability to recall or recite this type of information as declarative knowledge. Declarative knowledge is important. We need to remember the meanings of vocabulary words, our telephone numbers, the names of our bones, the milestone dates of history, our multiplication tables, and so on. Merely possessing a mental store of data is only one component of education, however. We also need to think and act on what we’ve learned through explanation, critical thinking, demonstration, and application—a category of cognitive behavior known as procedural knowledge.

Our eighth graders experienced the shift between declarative and procedural knowledge this week through a deceptively simple laboratory exercise: they boiled water. Although all of the students had observed water boiling on countless occasions before, this time was a bit different. Mr. Seston explained that they would be tracking the temperature of a beaker filled with H20 as it changed phase from solid to liquid to gas. The lab teams set up their apparatus and carefully lit their Bunsen burners. They charted the readings on their thermometers for nearly 15 minutes, recording the temperature every 30 seconds.

For the first two or three minutes, there was not much to report. Temperatures remained in the single digits. Then, as the ice melted, the students discovered that they could not call out their readings fast enough. The temperature rose quickly, reaching the mid-90’s and prompting comments, observations and ideas. “Look, there are bubbles on the edges. I think it’s going to start boiling,” someone noted expectantly. “Check out the condensation inside the beaker,” someone else pointed out. “It’s still not 100°,” came an impatient voice.

Finally, the water boiled. The students continued to track the temperature of their samples, and soon noticed that the temperature did not change. “It can’t go over 100°,” explained a student. “That’s the boiling point, and water can’t get hotter than that,” she added. “The flame is much hotter than 100°, but when the water gets that hot, it turns into steam.” There was a moment of thoughtful silence. “I wonder how hot the steam is,” she mused.

These eighth graders started their lab armed with essential declarative knowledge. They left with greater understanding of a basic thermodynamic process. They also left with more questions than answers. Procedural knowledge depends on knowing and wondering “how,” rather than knowing the facts. This is the essence of science.

February 3

There are several large sheets of chart paper hanging at the front of the first grade classroom, filled with statements about space. When she introduced a new science unit about the solar system several weeks ago, Ms. Angeles asked her students to share their thoughts and questions about the topic. The children’s responses demonstrated a great deal of knowledge, some important misconceptions, and a deep curiosity about the workings of the universe:
The world turns around, but you can’t feel it.
How does space have zero gravity?
The moon is a collapsed star.
Meteors are really huge.
Some space ships don’t have people in them.
Why don’t the planets fly up?
How many volcanoes does Venus have?
The sun is a star.
How many stars are in the Milky Way?
A person can’t survive on Pluto, even with a space suit.
How do the planets stay in a line?
Space never ends.

Ms. Angeles recorded all of these ideas and many more. Taken together, they reveal many essential attributes of scientific thinking: a fascination with quantity and measurement, an urge to understand complex phenomena, an interest in organizing and categorizing information, and a profound sense of awe.

The lessons and activities in this unit of study are designed to enhance each of those habits of mind. Ms. Angeles created a “Moon Bag” that goes home with a different child each night. Inside the bag is a collection of informational books about the moon and a slim binder filled with black construction paper pages and a calendar for the month to chart the phases of the moon. The children observe the moon carefully, then use yellow and white crayons or pencils to draw what they see. During their science classes, they discuss the moon’s changing appearance and learn the terminology to describe each phase: gibbous, waxing, waning, crescent.

The students are also learning about the sun, and how important it is to living things. At the beginning of the unit, Ms. Angeles brought two identical potted plants to class. The children took detailed notes about the appearance of each specimen in their science journals. Ms. Angeles then put one of the plants into a well-lit window, and the other one into a dark cupboard. The students made predictions about what would happen. Each week, the children compare the two plants. Their drawings and notes document the impact of a lack of sunlight, bringing the immensity of the solar system into a comprehensible experience.

January 27

Although it might sound like the name of a new science fiction movie or a video game, the title of this article actually refers to the software that drives our new Maker Bot, which has become a digital celebrity in the lower school lab. This week, a group of 7th and 8th graders will become the first students to program the Bot, as it makes its debut in the middle school technology/arts electives program.

We announced the arrival of the Bot last week amid great fanfare. In the days since it was installed in the lab, it has hummed away, producing a collection of precisely formed plastic objects under the careful supervision of Catherine Francis and Dolly Ryan. Catherine and her husband Dennis earned hero status at BDS for assembling the Bot from a kit of tiny parts, electronic components, and a daunting instruction manual. Thanks to their efforts, BDS is now the only school in the Boston area to have a 3-D printer in action. Catherine has put the machine through its paces; she programmed it to build components for itself and even created her own design to replace a broken part for one of our printers.

Rich Arum is leading the 3-D technology group. He explained the project that will occupy the students’ time for the next eight weeks. Using Google SketchUp™, an engineering program that allows users to build three dimensional digital images, the model-makers will create a miniature train based on the illustrations in Donald Crews’ spectacular picture book Freight Train.

Each student will be responsible for one car in the train. Manipulating the 360° views in SketchUp, they will make sure that the shape and dimensions of their cars are aligned to a specific scale. They will add details and unique elements to their cars as well. Once the designs have been completed, the files will be uploaded to Replicator G, which will convert them into blueprint images. The Maker Bot will then “print” the train cars according to the students’ plans. Finally, the models will be painted and assembled.

It may seem odd to characterize this process as “printing,” but that is exactly what is happening. Instead of ink, a small plastic wire feeds through a heated dispenser, which moves along the X, Y, and Z axes to deliver a specific amount of melted plastic onto a base platform. The finished product is prepared in layers from the bottom up, emerging millimeter by millimeter. It can be mesmerizing to watch the Bot, as many people have discovered.

Stay tuned for more news and productions from our exciting new device!

January 20

When Ms. Felton bought out the entire supply of Cornish game hens at her local supermarket on Sunday, she wondered if people in the store might wonder what sort of feast she was planning. After the store replaced its poultry inventory overnight, she went back the next day to purchase more hens, along with several pounds of baking soda, table salt, and powdered dish soap. All of the hens, packed safely in a travel cooler, arrived in the 4th grade science classroom on Tuesday morning. There was no roasting or frying involved.

This week marks the beginning of the annual hen mummification activity, a highlight of the Egyptian study unit that has engaged the class since before the winter break. Along with Mrs. Holman and Ms. Felton, the students have immersed themselves in the fascinating details of life in ancient Egypt, including an investigation of the embalming process that was used to preserve the bodies of pharaohs and other members of the civilization of the Nile.

The essential science concept in mummification is dehydration. Removing moisture from plant or animal tissue helps to prevent decomposition. The chemicals in salt act as efficient dessicants, a discovery that made Egyptian mummification possible. In order to give the students an opportunity to observe this principle, Ms. Felton introduced a preliminary dehydration experiment last week. The children sliced apples into precise wedges, then recorded several measures of the size of each apple sample. They buried some of the fruit in salt and left other slices to dry in the open air. By measuring the changes in the treated and untreated apples, the children were able to note the effects of the salt mixture.

The mummification process was more elaborate and exciting than the apples. The students had learned about the various roles performed in the Egyptian embalming ritual, and they were prepared to assume these responsibilities themselves. Wearing vinyl gloves, each partner pair was given responsibility for a packaged Cornish game hen. The Master of Ceremonies washed the bird carefully before delivering it to the Slitter, who coated it with a mixture of calcium chloride (table salt) sodium carbonate (the main ingredient in powdered dish soap), and sodium bicarbonate (baking soda). To further enhance the dehydration process, the Slitters made cuts in the skin of the hens, then pressed more of the salts into the openings they had created. Once the hen had been completely filled and covered with salt, it was sealed in a plastic bag to begin the drying process. Next week, the children will inspect their mummies, documenting any changes they observe. They will re-salt the birds and continue drying them. When the process is complete, the mummies will be presented in dramatic fashion!