Let me clear: doing the SAT problem of the day is better than doing nothing. Indeed, starting with something small is often a great way to get a reluctant SAT or ACT test-taker to begin the process. Nonetheless, it tends to create false confidence in both parents and students who are looking for a quick-fix to a big challenge.
In teaching test prep to Connecticut students through the last fifteen years, I can tell you that doing the SAT problem of the day – and nothing else – is equivalent to learning a few Spanish words each day in the expectation that this will be an effective way to learn the language. It is better than nothing but you need a more comprehensive approach.