I think a combination would probably be more fruitful at 6th grade. If
observatiional drawing is meaningful to the student or has an obvious
short-term purpose, it's much more likely that it will sustain interest. When
my daughter was in 6th grade, she was required to do at least one
observational drawing per week. After about 3 weeks it became very tedious
even though her drawing skills were above average.
Susan in OR