I agree with Lauras' comments, which were very well thought out and
"tested". Another approach is to know ahead of time which projects you will
formally assess (by a written criteria or rubric) which would involve your
written response to the childs work. This would also include the childs
assessment of his own work, which could be on a simple form with several
pointed questions about the concepts taught and as Laura says.."how the
problem was solved" (I use the same terminology). Students poetry and
expository writing about their work is an invaluable asssessment tool.
Other projects can be informally assessed by a simple checklist and group
discussion of displayed work. However you assess though, will heighten the
students and parents awareness of the VALUE of what they are doing!