CLAMP School Detectives:
"he CLAMP school, with its integrated curriculum from kindergarten to post-graduate studies, was founded by the largest of Japanese business empires, the House of Imonoyama. Funded entirely out of its own deep pockets, it was hoped that the school would be a haven for young men and women on whose shoulders our future would rest.
The School is open to any talented individual, irrespective of his or her lineage or financial standing and is known to count scores of singularly talented pupils. It is furthermore also famous for its harboring of a remarkable percentage of party animals. Not even the bright and talented minds of CLAMP School can keep the campus free of crimes and mysteries. Or can they? Join Nokoru, Suoh and Akira, our case-cracking kid detectives, as they save the day and even the odd damsel in distress!"
http://myanimelist.net/anime/1844/CLAMP_Gakuen_Tanteidan
Tantei Gakuen Q
"Kyuu is your average boy with a knack for logic and reasoning. Desiring to become a detective, he finds out about the existence of the Dan Detective School (DDS); a famed school where students are allowed to bear arms. Together with Megu, a girl with photographic memory, the martial arts master Kinta, the genius programmer Kazuma and the mysterious Ryuu, Kyuu tackles many well planned out crimes, always seeking the truth."
http://myanimelist.net/anime/407/Tantei_Gakuen_Q
Saint Tail
"Meimi Haneoka, 14, is a normal girl during the daytime, but during the night, she assumes the "position" of Saint Tail, a modern-day Robin Hood who steals from thieves and gives items back to their original owners. She is aided by her friend, Seira Mimori, a nun-in-training, and she is chased by her classmate (and soon-to-be love interest), Daiki Asuka (often called "Asuka Jr.")."
http://myanimelist.net/anime/1567/Kaitou_Saint_Tail
Angelic Layer:
"12-year-old Misaki Suzuhara has just gotten involved in Angelic Layer, a battling game using electronic dolls called angels. Even as a newbie, Misaki shows advanced skills as she meets new friends and enters Angelic Layer tournaments to fight the greatest Angelic Layer champions of the nation."
http://myanimelist.net/anime/52/Angelic_Layer
Magic Knights Rayearth:
"Three young girls, Hikaru, Umi, and Fuu, are transported to a magical world called Cephiro during a field trip to Tokyo Tower. They are soon greeted by Master Mage Clef, who explains to them that they have been summoned to become the Legendary Magic Knights and save Cephiro. The girls are less than enthusiastic about this idea, and only want to return home. Clef further explains that they must seek out the three Rune Gods to help them fight. He bestows armor and magical powers to each of them. They learn from Clef that High Priest Zagato has kidnapped the Pillar of Cephiro, Princess Emeraude. The Pillar of Cephiro has the sole responsibility of keeping Cephiro alive and in balance with her prayers. Without Princess Emeraude, Cephiro would fall into ruin. Hikaru, Umi, and Fuu must fight off Zagato's henchman and find the Rune Gods if they ever want to get back home. They soon learn that friendship and loyalty are the only things they can rely on in the crumbling Cephiro."
http://myanimelist.net/anime/435/Magic_Knight_Rayearth
Hope this helps. Good luck!!