Imagine that you were told to schedule three hours of entertainment for 20 people. You couldn’t even begin without knowing something about them. How old are they? Are they boys or girls or men or women? Do they share common interests, or are they strangers?
Even with your learning objectives written, you are still not ready to go ahead with your activities. You first must know your audience to devise the best way to get your lesson across. What abilities do your students have? Can they reliably ferret information from their text, or do most find such work too difficult? Unless your class has been grouped according to ability, you will find that the answer to both these questions is yes. If you move slowly enough for your lower students, you may lose control of your better ones as their attention wanders. Of course, going fast enough enough for them will leave the others behind. Individualized instruction supposedly addresses this problem, but in practice it is very difficult to achieve in a class of 25 or 30 students. You can divide the class into groups, but then your time is also divided. The better group moves faster than the slower, creating idle time. There is no complete solution to this problem, so you will have to learn to accommodate some level of discontent in this regard.
How much prerequisite information and skills do they have? If you are about to teach a unit on cloud formation, do they know about temperature change with altitude? Are they aware of the heat released by condensing water vapor? Do they even have the arithmetic skills necessary to do problems related to the temperature changes in rising air? It is quite possible, even likely, that you will have to include learning objectives in your lesson that go beyond the definition of the original unit.
How motivated are your students to learn the material? If the motivation is low, you may have to add activities or rewards which would otherwise be unnecessary. Perhaps you’ll have to reduce or eliminate long periods of individual seat work requiring self discipline, attentiveness and perseverance.
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