Start up a Dynasty with a decent 6 Star team (I choose Alabama, some other good teams to choose are OSU, Auburn, Texas). As soon as you select your team and start your Dynasty, head over to the "Set Up Recruiting Board" menu. No need to create prospects, so click on "Skip to Recruiting". Click on the search menu and change the Caliber to 5 star, then click A to search. Now navigate through the list of prospects and target each one that has an interest in your team (These prospects will be marked as green to the left of the player's name).
You will probably have around 20+ prospects left needed to complete your recruiting board, so this is time to head back to the search menu and change the caliber to 4 star prospects. Do the same as you did to the 5 star prospects until you complete your board. Once you have finished, simulate your season to the end.
After the season is over you will need to progress to the offseason. This is where you will complete all of the miscellaneous tasks in signing and various coaching contracts. No need to spend time doing all of that so just simulate it to the end. The achievement will unlock during week 5 of the simulation.
*In the Main Menu of your Dynasty, scroll over to the Dynasty Setup menu. From here you can change your recruiting difficulty to Freshman to make this achievement easier for you.*