If you're looking for manga similar to Nintama Rantarou: Saraba Ninjutsu Gakuen no Dan, you might like these titles.
Rakudai Ninja Rantarou is about a boy who wishes to become a chou-ichiryou-ninja (aka, the number one ninja). There is only one problem: he keeps failing. Together with his friends, they encounter mishap after mishap as they seek to eventually graduate from the first grade.
In the Hidden Leaf village of Konohagakure, there’s a hot-blooded ninja in town! Rock Lee is an energetic boy, whose complete and utter lack of talent in using ninjutsu techniques has given him an unstoppable belief in hard work and self-determination. Driven by his admiration for his teacher, Guy, Lee trains day and night to become the strongest ninja despite his inability at the most basic ninjustu. But even outside of his missions, whether he’s trying to beat his rival, or attempting to confess to the girl he likes, Lee stampedes through life at full-throttle never letting anything slow him down.