How long do I need to be in Kumon and how effective is it?

Ok, so I am an incoming freshman and my parents want to send me to Kumon to improve in reading. But really, the help I need (my parents know this too) is in more advanced reading comprehension and especially inferring things from the text. I am aware you have to take take a placement test; and from what I've been reading online, it seems like you are generally placed at lower levels, and to advance you need perfect scores on all the worksheets. Is that correct? And how far is it to get to the "level" with critical comprehension and inferences? Because from what it sounds like, I'll start with basic stuff and won't get to take what I feel I need (at least for a while); and as a result, I'll be there forever( figuratively speaking). Just need to know. Thanks.