A good student would do well regardless, a bad student would do bad regardless. Cell phones might help a bad student do a little less bad, but only a little.
For the middle, it really depends on the material covered. if it's cumulative, then results might not change as much. if it's "learn and forget", then it might be testing the wrong incentives.
For the middle, it really depends on the material covered. if it's cumulative, then results might not change as much. if it's "learn and forget", then it might be testing the wrong incentives.