Why is مُعَلِّمَاتٍ genitive in تَحَدَّثْتُ إِلَى مُعَلِّمَاتٍ?

Noun Case Classes: Type 2 — Sound Feminine Plural

• Because it follows the preposition إِلَى
• Because it is the subject
• Because it is a direct object
• Because it is indeclinable