This is a provisional news based on unofficial sources.
The official announcement was made on Feb 12th.
Multiple blogs reported that Kodansha announced the second season of Negima OVA at the preview event of "Mahou Sensei Negima! OVA Shiroki Tsubasa Ala Alba". It will be four-volume series and bundled with manga "Mahou Sensei Negima!" Tankoubon. The first volume will be released this summer. If the sales of the new series are sufficiently good, they will make an anime movie of Negima.
The story of the new OVA will correspond to the Magic World arc of the manga.

Staff
Director: Shinbou Akiyuki
Character Designer: Jitsuhara Noboru ("Mahou Sensei Negima! OVA Shiroki Tsubasa Ala Alba", "Negima!?")
Production Studio: SHAFT

The total sales of the first OVA series were 245,000 copies.

Edited on Feb 15th==========
Akamatsu Ken announced in his web diary that the total length of the new series including the possible movie will be approximately 3.5 hours.

Source: Kuroneko news site
Source: Coco's blog
Source: Zaregoto blog
Source: Renkinba blog
Source: Akamatsu's diary
Source: Negima OAD Official Website