The story follows the "strongest juvenile delinquent", Oga Tatsumi, a first year in "Ishiyama High" the school for delinquents. One day while sleeping next to a river he sees a man floating down it, he pulls him to shore and the man splits in half revealing a baby boy. This boy is the son of the demon king and he has been chosen as the one to raise it with the baby's demon maid Hilda. The story follows his life with the child and at the delinquent school.
Perriot studios had to give something up and Beelzebub was that something. There are many extraneous reasons behind it, but these are the ones that were made most clear.
1. There was too many fillers. According to the producers of the anime, these fillers were time consuming and a waste of money as at the end of the day the anime failed to accomplish the task of actually adapting the manga.
2. Perriot studios (the guys who draw the animation) had other bigger commissions to make way for and this meant they had to sacrifice the losing battle that was the Beelzebub anime in favour of the manga and anime they have had longer contracts with. You will note that all of a sudden Bleach has also reached its end as an anime and this is mainly because the anime has come too close to the manga - so like Beelzebub it is stuck in a similar situation.
The manga is sooo much better than the anime and instead of mourning the loss of the visual action, rather read Beelzebub. It's what I have been doing since it came out in anime and to be quite honest the manga is better by far.
