Mary Gowans, 42, is on trial for charges of sexual assault and sexual interference for alleged incidents that took place in 2010 involving a student who is now 18 and cannot be identified.
The court has earlier heard testimony that the pair often spent time alone together outside the classroom. He babysat her children and they frequently ran together.
Earlier in the week, the former student also testified Gowans exposed her breasts to him and that the pair kissed and were involved in heavy petting sessions, all claims she has denied.
Crown prosecutor Soula Olver asked Gowans on Friday why she would choose a teenager and former student as a running partner.
Gowans said the invitation to run with her was open to all her students. She admitted she ran alone with the boy who she said became "like a member of the family” and babysitter to her children.
Olver asked why Gowans would have the boy over to babysit when her husband worked from home.
“Why would this young boy ... spend time with your son ... when your husband was at home?”
Gowans answered: “I thought it would be a good time for him [her son] to interact with a boy closer to his interests.”
Gowans was also asked Friday about a bet she allegedly made with her student, in which winning meant he was allowed to spray her shirt with water, making it see through.
On the stand, Gowans said her student was just simply acting like a jerk and said the incident left her “annoyed.”
When asked why the boy was allowed to continue to babysit after the shirt-spraying incident, Gowans answered: “Boys are silly. They do silly things sometimes.”
Gowans, who admitted she has breast implants, also denied that she ever discussed them with her former student.
The trial, which is being conducted by judge alone, will continue next week.