Your points 3 and 4 suggest that no answer to points 1 and 2 would satisfy. To me, that's a problem-- it means that no action they take or promise they make can satisfy, because promises can be broken and actions undone and you don't trust them not to. As a result, it is illogical of Google to address any concern you raise. I think that's a loss.
1 - Has Google always adhered to it since it was written? Have they ever violated it? If they have, in which way, in regards to whom and by whom? How would I get access to this information? Are independent, respected consumer-protection watchdogs auditing Google to make sure they're adhering to their own policy? The same questions apply to all of the companies Google shares this data with.
2 - What measures has Google taken to combat de-anonymization ( https://en.wikipedia.org/wiki/De-anonymization ) of their data?
3 - Google can change their privacy policies at any time, and all this pledge requires is that they provide notice and unspecified "choices" to account holders. Nothing prevents those choices from being effectively meaningless or powerless against future data sharing or use.
4 - Even if Google adheres 100% to the letter and spirit of their student privacy pledge, the data they collect could still be leaked or stolen, in which case the students are screwed. The only real way to prevent that is not to collect data in the first place.