The six include two builders who added an extension to the upper floor of the Scuola Francesco Jovine in San Giugliano di Puglia and a municipal surveyor who issued a safety certificate when the work was done. Experts believe that the extra weight of the extension may have weakened the structure.
Although the village of San Giugliano in central Italy was at the epicentre of the quake, the school was one of just three buildings that collapsed.
Since the quake, a number of surveys and reports have come to light suggesting that around half of schools in Italy are unsafe or lacking safety certification.
Earthquakes are common in Italy. In December an earthquake brought down part of a stairwell in a school in Sicily. Pupils had evacuated the school only minutes before, after the first tremors.