This is the preterit tense. It's "ellos prepararon."
lecciones or enseñanzas
explique la lección
You say, "Hola estudiantes"
You would say "Tus estudiantes".
preparar la comida
preparar la comida
Buenos estudiantes.
By asking the students questions and also by listening to what they say and the questions that they ask during a lesson. Even by just observing the students as a lesson progresses a teacher can get a feel for what they are learning. If a lot of students look confused, a teacher can know they are finding it difficult to understand. Teachers can also give a test after the lesson or a task to do to see how much they have learned.
en el medio de la clase
By asking the students questions and also by listening to what they say and the questions that they ask during a lesson. Even by just observing the students as a lesson progresses a teacher can get a feel for what they are learning. If a lot of students look confused, a teacher can know they are finding it difficult to understand. Teachers can also give a test after the lesson or a task to do to see how much they have learned.
Piano de cola
hay veinte estudiantes.