Describe the three key motions of the Earth-Moon-Sun system (Earth's rotation, Earth's revolution, and the Moon's revolution) with their approximate periods.
The Earth-Moon-Sun system involves three motions that are easy to mix up. Earth rotates on its own axis about once every 24 hours, causing day and night. Earth also revolves around the Sun, taking about 365.25 days, which is why a year is about 365 days long.
The Moon revolves around Earth about once every 27.3 days. But the full cycle of Moon phases (new moon back to new moon) takes about 29.5 days, a bit longer, because Earth has also moved along its own orbit during that time, so the Moon needs extra time to catch up to the same Sun-Earth-Moon angle. That 29.5-day cycle is close to why we call it a "month."
Mastery looks like: They match each of the three motions to its cause (day/night, year, month) and approximate period.
Common stumbles: Confusing rotation (spinning in place) with revolution (orbiting another body); assuming the Moon's orbital period and its phase cycle are exactly the same length.