Facilitating active learning through a thematic science curriculum

The lessons in this study also provided many opportunities for students to develop their problem-solving and thinking skills. Kirkwood (2000) asserted that "problem solving is a goal-oriented process which requires the integrated use of a range of higher-order thinking skills" (p.511). He further elaborated that these thinking skills included generating ideas, making interpretations and judgments, and using strategies to mange the complexity of situations. The "Clean Water" theme in this study was designed to develop students' thinking and problem-solving skills. Students were intentionally not given with detailed descriptions of experiment set-ups and procedures during practical activities. They frequently needed to make their own decisions in choosing appropriate apparatus from a equipment list provided in the laboratory. Then teachers would encourage and challenge their students to design experimental methods and solve problems on their own.

In the lessons about filtration, teachers introduced different types commercial household filters to the students. Students were challenged if they could make their own filter columns, which worked as well as commercial ones, by using common materials readily available at home or in shops. It was found that most teams could make their own designs with careful considerations and sound reasons. They understood the relationships among the sizes of materials used, the outcome of the purity of filtered water and the speed of filtration. Students usually had their own theoretical and empirical reasons for the choices of materials or setting up the sequences and thickness of layers. Most reasons given were quite logical in terms of scientific and technological principles. Two examples of students' designs were shown below.

Figure 1

Figure 2

The team designing the filter in Figure 1 reported that activated carbon should not be placed at the highest layer and also lowest layer of the column. The explanation given was that activated carbon would come out with water when it was placed at the lowest layer because the size of its particles was very small. Moreover, the impulse produced by falling water would make activated carbon, if placed at the top of the column, diffuse into other layers. The other team claimed that the thicker the layers, the purer water would be filtered. But this team still limited the thickness of each layer to 5 cm in regard to the size of a home-use filter (Figure 2). By comparing their own filter columns with commercial ones, students could comment on the quality, technical aspects and prices of different bands of commercial filters. This activity really engaged students in solving a practical problem by giving them flexibilities in setting up the equipment. In fact, students were provided with opportunities to think and solve the problem during such an open-ended practical work. Students reported that they were very proud of the filtering effect of some of their hand-made filters which were quite satisfactory comparing to some commercial filters.

A very distinguished outcome was also observed in the lessons about distillation. Students were asked to design their own setup to collect a few drops of water from the steam generated from boiling water. Varying in time spent, most groups finally succeeded in collecting a few drops of water on a watch glass by using a piece of glass slice. Then, a competition was held - to collect as greatest amount (more than 20 ml) of condensed water as possible within a specific time interval. Without showing students the standard condenser in the laboratory, this activity intended to facilitate students to think how to solve the technical problems of collecting distilled water. Discussing, trying out, modifying and re-trying, most teams in the classes observed could finally collect significant amount of distilled water. Figure 3, Figure 4 and Figure 5 shown below were the methods devised by a team in the class of Ms. Ting (pseudonym).

It would be very amazing that students could figure out their own methods to solve the problems of cooling down hot stream effectively and collecting significant amount of distilled water, say 10 to 20 ml. This team initially used some test tubes to collect condensed water. As shown in Figure 3, students put test tubes alternatively over boiling water to collect steam and a crucible to collect condenser water from the test tubes. They explained that several test tubes were used because they intended to increase the area for condensing water. They later replaced the crucible by a watch glass as they found that the crucible was not clean enough. This team soon discovered it was inconvenient to move test tubes around. They thought that there should be some more convenient ways that condensed water would pour down automatically. One of the team members put the test tube the other way around and found that condensed water flowed down automatically. The problem was not yet solved as students soon found that the speed of condensation reduced when the test tubes became warm due to hot steam. To solve this problem, one of the students put some tap water into the test tube for cooling as shown in Figure 4. This team still found that water in the test tubes would get warm after a while. They then decided to put ice into the test tubes (Figure 5). This team managed to collect about 30 ml of condensed water.

During the post-experiment discussion, students of this team reported that some of the distilled water they collected might not come from the water they boiled. Students found that the test tubes containing ice water would collect vapour even when they were not placed on the top of the boiling water. "In your opinion, where does the water come from?" the teacher asked. "Maybe vapour in the laboratory", they answered. The whole class concluded that the set-up in Figure 4 was better than that in Figure 5 when the teacher asked them to choose the best method adopted by all teams. The teacher further asked the class if there any methods could solve the problem of preventing the test tubes containing tap water from getting warm. One student proposed that water inside the test tubes would be changed for every 10 minutes. Grasping this golden opportunity, the teacher said that it would be more convenient if they could make water keep on running in and out the test tubes continuously. Then a student suggested to connect tap water to one end of a tube and make water flow out at the other end. In the closure of this lesson, the teacher demonstrated the standard condenser in the laboratory.

Students were proud of their designs some of which were close to what scientists did in the lessons about filtration and distillation. As a matter of fact, students' learning and achievements in these lessons were so superb that they achieved to solve the problem well and designed setups which were comparable to standard condensers in the laboratory and commercial filters. In Hong Kong, each school is usually equipped with one condenser. Traditional class practice of teaching distillation is to demonstrate the use of the standard condenser to obtain distilled water by the teacher. Students seldom have the opportunity to do the experiment of distillation on their own. The concept of filtration was traditionally taught by performing an experiment of filtering water by using a funnel and some pieces of filter paper. The teaching focus sometimes shifted to teach students how to fold filter papers onto a funnel. The teaching strategy adopted in the unit "Clean Water" of the JSSC was able to engage students in some hands-on and minds-on activities. In the cases of teaching filtration and distillation, students had good opportunities to think and work out their ways in solving problems during the experiments.