Children’s use of diverse strategies makes it essential that they choose appropriately among the strategies.
To choose appropriately, they must adjust both to situational variables and to differences among problems.
Situational variables include time limits, instructions, and the importance of the task.
For example, in a magic-minute exercise, it is adaptive for children to state answers quickly, even if they aren't absolutely sure of them. Similarly, if it's very important to be correct in the particular situation, then checking the correctness of answers becomes more worthwhile.
At least from second grade onward, children shift their choices appropriately to adapt to such situational variations.