<em>Los estudiantes que yo conozco no</em><em> fueron</em><em> nunca conmigo</em>
The original sentence stands for the simple present tense. Recall that this tense is used to talk about habitual actions or routines. So van is the conjugation of the verb ir that matches the third person plural (ellos - they) in this tense. To write this sentence in the preterite, we must changa the conjugation of the verb ir from van to fueron. Recall that we use the preterite tense to describe actions that took place or were completed at a certain point in the past. Finally:
<em>Los estudiantes que yo conozco no</em><em> fueron</em><em> nunca conmigo</em>