One who initiates the pupil into Gayatri is called the Acharya.
Manu Smriti 2.140. They call that Brahmana who initiates a pupil and
teaches him the Veda together with the Kalpa and the Rahasyas, the
teacher (acharya, of the latter)
2.141. But he who for his livelihood teaches a portion only of the Veda, or also the Angas of the Veda, is called ...
Gradation of teachers based on teaching levels :
The teacher who gives you information only is .......
The one who imparts knowledge by combining information is....Upadhyaya
Skills are imparted by ....."Acharyas". Composers and teachers of bhashyas are also called Acharya
The teacher who is able to give an insight into the subject is .....