Patience... I know it's hard, but gubment works on gubment time, which can be painfully slow... I hope that you have been assigned a good mentor (OJT trainer) and you have been getting out in the field a fair amount. I also hope you have had ample learning opprtunities while in the office. Exposure to "Demand Work" like handling Complaints, Occurrences, Pilot Deviations, and "hands on" experience with office automation (i.e. ATQA) will be very helpful. If the office workload is "light", Pick a topic in the 8900.1 to read, then to go to your mentor to discuss and get at least Level 1 signed off. With over 100 possible tasks, there is bound to be something new to learn while you wait. Some tasks can be "simulated" per the OJT Order. You should never be "bored" in the office as an apprentice ASI. If you are, then something is dreadfully wrong.
String training is a necessary "checkmark" in the box, but is certainly not the "holy grail". The best "takeaway" from string is the peer networking aspect imho...
Hang in there! Your first year will be a distant memory sooner than you think!