Hi Debra,
Most people can absorb only so much before their minds begin to wander, lose interest, or get distracted. Breaks help prevent this. A break every 20 minutes? Some may say that's way too often. Perhaps so. But a "topic" or "activity" break every 30-40 minutes may not be so unreasonable. I really don't know how frequent breaks should be, but I know students perform better and stay fresher, more open to the lesson when frequent breaks are given - even a short 5-minute "stand up and think about something else" break.
Barry Westling
