effective

An effective strategy, treatment, method, etc is one that works well as planned.

Example: Teachers are using instructional strategies that are most effective in helping students learn.

If you have effective command, consent, control, etc., you have it in practice but not officially.

Example: The students had effective control over what the teacher would include on the test.

If a law, agreement, change, etc. becomes effective, it officially begins.

Example: The new rules about ball size are effective next season.

You use effective to tell when something starts officially.

Example: Effective next week, all employees will wear the new uniform.