Children use more private speech when tasks are:

1. Private speech helps children regulate behaviour. 2. Research shows children use more private speech when asked to do more difficult tasks. 3. They also use more when working without a teacher's help. 4. So difficulty increases private speech. **Why not the others:** Quite easy tasks and mastered tasks need little self-guidance, and group work gives help from others. _Source: Wikipedia, "Private speech", section "Behavioral self-regulation and emotion regulation" (revision 1378894484)_