Thus Taba's teacher is required to make quick and subtle judgements about the cognitive processes of her pupils, about when the discussion has got to the point that an attempt at generalization is called for. But that is not the teacher's only burden; she also has the problem of individual differences. Even if she possesses the teaching strategies for implementing the principles of sequence, some of her pupils need more concrete instances than do others before they are ready for the leap to formal or abstract thought. Indeed, as Taba says:
'It is not beyond possibility that by far the most important individual differences may be found in the amount of concrete thinking an individual needs before formal thought can emerge.'
The demands of cognitive validity and individual differences