In a previous blog entry I asserted that instruction without concern for metacognitive construction of understanding is imperfect. You can lead a horse to water, but the learner must want to learn. This is why so many well-meaning examples of constructivism go awry. Too much focus is placed on engagement at the expense of the guided inquiry. This does not mean that the need for engagement isn't crucial, but you have to do more than just get a student's interest.
Here are some other examples of "The Monotillation of Traxoline" if not followed up by guided inquiry:
My point isn't that these activities are pointless. They can be very useful, but they are not science lessons in and of themselves. They are the beginning of understanding, and only that if they are framed as an introduction to phenomena that beg explanation. Students must be guided by inquiry from the hands-on experience used to engage them into the content lesson that will fulfill their thirst for explanation.
They must still construct their own understanding, but they cannot do it on their own. Teachers need to be prepared to be flexible, and they need to be prepared to present content at the crucial time in the lesson.
All too often, hands-on activities are used at the end of a content lesson and expected to demonstrate what has been learned. This tends to make the "experiment" either superfluous or distracting depending on how well, or poorly, the content has been delivered and related to the activity.
Science starts with an observation that presents a problem in need of explanation, proceeds to collect all relevant information on the problem, and then controls experiments that test hypotheses formed to provide explanation. Constructivism poses the same guidelines for learning about science.
It's okay to say, "I don't know" to a student's question, if fact it is important to do so, so long as that response is followed by "let's find out". Science is about the finding out. The knowledge accumulated by centuries of science in practice is needed to solve new problems. No one has all of the answers, but everyone can learn to think scientifically. This includes the skills of knowledge acquisition and problem solving.
Start with a hands-on activity that presents a problem in need of explanation. Follow this with content discovery guided by inquiry, by whatever methods are appropriate. Finish by putting this information into a larger explanatory framework.
Without each of these steps, the hands-on activity is just like the monotillation of traxoline.