Earlier this year, Shelia Cotten and coauthors Hale, Moroney, O’Neal & Borch published an overview of their data from surveying 27 schools during the first year of the city-wide OLPC project in Birmingham, AL.  In the 2008-2009 school year, 1st – 5th Grade students and teachers, in every public primary school in the city, received XO laptops via this program. — amounting to over 15,000 students and teachers. and every public primary school in the city.
The paper, “Using Affordable Technology to Decrease Digital Inequality“, appeared in Information, Communication & Society Volume 14, Issue 4.  From the summary:
[F]ourth and fifth grade students at 27 Birmingham City schools were surveyed just prior to receiving the XOs and then again about 4.5 months later. A total of 1,202 students were matched between the two surveys… students who used a computer to do homework before receiving the XO, tended to make greater use of the XO and felt it helped them in their education. Teachers’ use of the XO was also an important factor. Students who reported their teachers made greater use of the XOs in the classroom tended to use the XO more and felt that the XO had a positive impact on their education.
These findings highlight the importance of training teachers to make effective use of new technology and the need to develop curriculum to integrate computers into the classroom. Dr. Cotten is currently leading a National Science Foundation funded project that helps… teachers receive training which builds technology-teaching capabilities so that students develop the attitudes and the skills necessary to succeed in a technologically advanced society.
Their research has continued since then, and they will also publish about longer-term results.