What is the voice of the verb in the sentence: "Mrs. Walker told scary stories to her class."?
It is an active voice sentence.
To find out if the sentence is in active or passive voice you have to look at the form of the verb.
The passive voice sentence has a verb in form
to be + Past Participle.
Verb to be can be used ia any tense.
Many houses have been built recently. (Present Perfect)
Scary stories were told to the class. (Past Simple)
A new road will be built next year. (Future Simple)
In given sentence the form of the verb is told, so it is an active voice sentence (in Past Simple tense)