The problem is that we often use the techniques with children for whom the method is either too hard or too easy. Also, we often use a technique past the point of its effectiveness. For the average teacher, to find the perfect match between a child's needs and a certain technique is difficult, given the demands of the classroom. Children with not identical but those with similar needs can benefit from the same type of activity, although to a different degree. Children with different needs will require substantially different approaches.
Ongoing assessment can help teachers to further adjust techniques.