The time when it is necessary or appropriate to use different tools in a class varies. We use compasses, protractors, pencils and crayons in our classrooms but not all at once in every subject. The same is true for computers. Computers are also just tools and their usefulness will vary from time to time and from subject to subject. For example, we are likely to use word processors more often in language arts at first.
Spreadsheets fit nicely into math.
Databases can be used for information manipulation in many subjects, but are probably easiest to introduce in Social Studies and Science where a considerable amount of data needs to be assembled and manipulated form time to time. However, it is important to remember that we don't need to use these tools every day in every subject and all year long. It will become necessary for teachers to plan for computer use in long range plans so that they are working on the appropriate project at the time when the computers are available to them. In this case the teacher could use the lab period for math for two months, for social studies for the next two months, and so on The lab could be timetabled by grade rather than by individual class. For example 3rd period each day could be booked for grade 3 classes, and the grade 3 teachers would decide between themselves which one would use the lab on any given day.