The straight answer to this question is 'Yes', but unless you have worked through the remaining four grades in detail it will be better to commence at the beginning, or at the beginning of the next grade to the last one you have studied. The big problem lies in the fact that in general theory work topics are cumulative, most of the important disciplines being introduced in the lower grades: this means that if you don't start at the beginning it is highly likely that you will miss some extremely important information or methods which you will need for later in the course. Trying to save time by skipping grades is not good time economy; most students who have missed out parts of the course have not completed it. A better solution is to work through the course, but to purchase the Course Materials only for the lower grades (in this way your lower grade work will not be marked and monitored, so your guarantee of success will not be as great, but your time will be saved). If you have sufficient time it is always best if students follow the entire course, and will always produce the highest results.