Dyfed-Powys Police are looking into claims, concerning former members of staff, that abuse took place at Rhydygors School between 1976 and 1986.
Operation Almond is focussing on claims of physical and sexual abuse.
It is also looking at allegations of abuse at Cartref-y-Gelli children’s home in Carmarthen between 1986 and 1990.
Rhydygors school provides special education for pupils with social, emotional and behavioural difficulties.
Dyfed-Powys Police said allegations concerning the school were fully investigated when they were made in 2000 and were referred to the Crown Prosecution Service (CPS).
However, no criminal proceedings were instigated at that time.
Further allegations were made in 2012, which also included claims of abuse at Cartref-y-Gelli, which prompted the current investigation.
Carmarthenshire County Council said it was working closely with Dyfed-Powys Police to fully investigate the allegations.