There is a big problem, from the perspective of assessment, with the biologist's visit to Percy's Scarsdale classroom: it isn't clear ahead of time what particulars will be covered. An authentic learning experience simply does not lend itself to objective assessment. A biologist can lead the curiosity of the class in whatever direction it is wont to go only as long as there is no standardized test or Biology II class waiting to be cued up.
Where am I in the content of the book?