This book focuses on a process which is generally known as teacher planning. Teacher planning is assumed in this work to serve two important functions. Its first function is to make teacher knowledge influence teacher intervention. Its second function is to promote the development of teacher knowledge. The first function has been much more discussed in the available literature than the second function, as presented next. Because of the links between teacher planning and action, teacher planning has a high potential as a vehicle for theory to be applied in teaching. These links include, at a certain grain size, the influence of the plan on opportunities to learn, content coverage, grouping for instruction and the general focus of classroom processes. Micro-level teaching processes such as specific verbal behaviour are not significantly influenced by planning, as they are mostly determined by interactive decision-making.