Sentence:  The European Roma Rights Centre in Budapest, which is representing the children - from the north-eastern city of Ostrava - said that the education ministry and local authorities had for decades "perpetuated a system which routinely brands disproportionate numbers of Gypsies as mentally <WSD>retarded</WSD>". 
Meaning of the word marked with <WSD> tags:  Having mental retardation; mentally deficient or underdeveloped.