Son started receiving calls from advisors the summer before junior year, after a good summer in the Northwoods league. He selected his, not from a call but from a referral, right after Christmas his junior year. He said he may have worded a few things differently during scout interviews if he had had an advisor earlier. Going forward he followed his advisor's advice.
I had been told by someone in the baseball world that you don't need an advisor unless you are a top prospect. However, for us, he was very helpful, and how did son/us know at the time that he would have been drafted 1-10 rounds? Maybe it was BECAUSE of the advisor? Son had said from the beginning he would go for slot, so there was no bonus negotiations that we know of. Advisor was helpful the day of the draft when teams started to call and "low ball" bonus offers to get him to commit.
His agent has been invaluable in insisting the organization use a top surgeon for son's surgery, and providing other organizational information to son when necessary.
We (the parents) will hopefully get to meet him this fall after almost 3 years and texts. I would think a HS player's parents would be more involved than we were. We let son choose the person he was most comfortable with. It was his ballgame.