Derby beat Carlisle 2-0 to secure promotion back to the Championship, while Cheltenham couldn't get the win they needed at Stevenage that would have seen them survive.
The Rams knew all they had to do was avoid defeat against bottom side Carlisle, and they got off to the best possible start, scoring after just five minutes through Max Bird.
Bolton, who were the side needing Derby to slip-up, raced into a lead at Peterborough themselves to keep the pressure on the Rams, but Derby sealed promotion with a second goal just before the hour mark that meant it was party time at Pride Park.
The Trotters, who ended up drawing 3-3 on the final day, have to settle for third place then, and will take on Barnsley in the play-offs, who conceded a late equaliser against Northampton to see them drop from fifth to sixth in the final standings.
Fifth place was taken by Oxford, who did what they needed to in winning 2-1 at Exeter. The U's went into the game outside of the play-off places, needing a win themselves and for Lincoln not to beat champions Portsmouth, and that was how it went, as the Imps lost 2-0.
But, it could have been so different, as Lincoln missed a penalty early in the second half that would have seen them go 1-0 up.
Blackpool, also in with a chance of pinching a play-off spot, went 1-0 up away at Reading only to fall 3-1 behind and eventual lose 3-2, meaning it will be another League One campaign for them.
At the other end of the table it was a battle between Burton and Cheltenham to avoid the drop, with the latter needing a win and for the former not to win in order to survive.
Burton did not win, they got thrashed 3-0 in fact at already relegated Fleetwood, but Cheltenham couldn't get the win they were looking for, losing 2-1 at Stevenage, and as a result they drop in League Two.