As per the information from NCERT, "From the academic year 2012, the MHRD  
has shifted NTS examination from class 8 to class 10" Details will be  
announced on 3rd week of July 2012.
http://dsert.kar.nic.in/index.asp

Exact details have still not come out. there is a meeting scheduled on 13  
July at NCERT on below mentioned points :
1. Possibility of conducting NTSE in both the classes ( Class 8 and 10 ) at  
least for this year .
2. Minimum percentage criterion in last class to be eligible to write NTSE
3. Discussion on increased no of scholarship as well as the amount.
4. time frame when the increased scholarship be applicable.