A fragment from the lost works of Athenaeus of Attalia, preserved in Oribasius, libri incerti 39:

“From six and seven-years, give your children over to gentle and benevolent elementary school teachers. Educators who teach using a combination of persuasion and compassion, and who offer lots of praise as well, are successful teachers and will encourage the children more. Also, their teaching is accompanied with joy and relaxation, and when the soul is relaxed and joyful, it contributes a good deal to the body’s thriving. But those educators who are relentless with their punishments will end up making the children miserable, fearful, and hostile to education. When they thrash their students, they are forcing them to learn and memorize things at the exact same moment they are being punished—in other words, when the children are least likely to be able to think! Also, don't oppress new students for the whole day with lessons. Instead, give over a greater portion of the day to amusement. In fact, we see among children who are pretty strong and mature for their age that, when they are always working hard at their lessons, their bodies become thoroughly corrupted.

“Twelve-year old children should go to geometry teachers as well as elementary teachers, and they should start taking gym. Also, their helpers and supervisors should be sound-minded and not completely inexperienced. This way, you know they will keep track of the proper times and portions of food, exercise, baths, sleep and everything else that has to do with being healthy. I feel I need to say this because most people spend a lot of of money hiring someone to groom their horse, making sure to choose a person who is careful and experienced; but, regarding a supervisor for their children, the same people will hire someone with no experience, or who is completely useless, and who cannot help at all in matters of life.”

ἀπὸ δὲ τῶν ϛˊ καὶ ζˊ ἐτῶν τούς τε παῖδας καὶ τὰς κόρας γραμματισταῖς παραδιδόναι πραέσι καὶ φιλανθρώποις· οἱ μὲν γὰρ προσαγόμενοι τὰ παιδία καὶ πειθοῖ καὶ παρακλήσει διδάσκοντες, πολλάκις δὲ καὶ ἐπαινοῦντες, ἐπιτυγχάνουσι προτρέπονταί τε αὐτοὺς μᾶλλον καὶ μετὰ χαρᾶς καὶ ἀνέσεως διδάσκουσιν (ἡ δ’ ἄνεσις καὶ χαρὰ τῆς ψυχῆς εἰς εὐτροφίαν σώματος μεγάλα συμβάλλεται)· οἱ δ’ ἐπικείμενοι τῇ διδασκαλίᾳ καὶ πικροὶ ταῖς ἐπιπλήξεσι δουλοπρεπεῖς αὐτοὺς <καὶ> καταφόβους ποιοῦσι καὶ ἀλλοτρίους πρὸς τὰς μαθήσεις· δέροντες γὰρ μανθάνειν καὶ μνημονεύειν ἀναγκάζουσιν ἐν αὐταῖς ὄντας ταῖς πληγαῖς, ὅτε καὶ τοῦ φρονεῖν ἔξω γεγόνασιν. οὐκ ἀναγκαῖον δ’ οὐδὲ δι’ ὅλης τῆς ἡμέρας θλίβειν τοὺς ἀρτιμαθεῖς, μερίδα δὲ διδόναι παιδιᾷ αὐτῶν πλείονα· ὁρῶμεν γὰρ καὶ τῶν ἰσχυροτέρων καὶ τετελειωμένων ταῖς ἡλικίαις τοὺς ἐπιμελῶς καὶ ἀδιαλείπτως προσεδρεύοντας τοῖς μαθήμασι καταφθειρομένους τοῖς σώμασιν.

τοὺς δὲ δωδεκαετεῖς τῶν παίδων πρός τε γραμματικοὺς φοιτᾶν ἤδη καὶ γεωμέτρας καὶ τὸ σῶμα γυμνάζειν· ἀναγκαῖον δὲ νουνεχεῖς εἶναι τούς τε παιδαγωγοὺς αὐτῶν καὶ τοὺς ἐπιστάτας καὶ μὴ τελείως ἀπείρους, ὅπως τούς τε καιροὺς καὶ τὰς συμμετρίας ἴδωσι τροφῆς, γυμνασίων, λουτρῶν, ὕπνου, τῶν ἄλλων τῶν κατὰ τὴν δίαιταν· οἱ γὰρ πολλοὶ τῶν ἀνθρώπων ἱπποκόμους μὲν πλείονος ὠνοῦνται τοὺς ἐπιμελεῖς καὶ ἐμπείρους ἐκλεγόμενοι, παιδαγωγοὺς δὲ τῶν τέκνων καθιστᾶσι τοὺς ἀπείρους καὶ ἀχρήστους ἤδη γεγονότας καὶ μηδὲν ἔτι δυναμένους ὑπηρετεῖν τῶν κατὰ τὸν βίον.

Oribasius, libri incerti 39.3-5, CMG VI 2,2 138,28-139,15 Raeder