Here is the NFL page about the program they have in place with the NCAA to advise players as to whether they should stay in school until graduation. There are several separate programs housed under the umbrella, players have opportunities to speak with the NFL, scouts, etc. in addition to their own coaches.
The above page also describes the role of the college advisory committee, which actually provides NFL scouting reports to the committee so they can advise individual players.
COLLEGE ADVISORY COMMITTEE
To help underclassmen that are considering entering the draft, the NFL developed the College Advisory Committee, where NFL scouts project where a player will likely get drafted — if at all.
The evaluation committee has correctly projected 73.7 percent of first-round picks, 85.4 percent of second-round picks and 52.9 percent of third-round picks.
The board evaluates up to five underclassmen from each school, though evaluations for additional players are considered on a case-by-case basis. Limiting the number of players the committee evaluates allows the scouts to focus on those players with a realistic chance and provide more accurate projections.
The board’s assessments keep some players from making an ill-advised decision to leave college early. In the majority of cases, student-athletes are encouraged to stay in school for another year to get their degrees and improve their draft stock.
As more underclassmen declare for the draft, the advisory committee’s role becomes increasingly important. In 2014, 44 of the 107 underclassmen who entered the draft went unselected. That follows a three-year trend where more underclassmen enter the draft, and fewer get drafted.