Tantei Gakuen Q

Detective School Q is the story of a group of young students from Class Q of Dan Detective School (DDS), a prestigious and renowned detective academy founded by Morihiko Dan, the most famous detective in Japan, and the adventures and mysteries they unfold and solve together. They eventually work against Pluto, a mysterious organization which creates almost fool-proof plans that only a handful of detectives can solve.

(Source: Wikipedia)