Should  a client with Scoliosis perform the side Plank? I think so, as a strong side plank, when  matched with a strong plank and a good “brace” means the torso is “nice and locked down” ( highly scientific stuff)
The paper, “Serial Case Reporting Yoga for Idiopathic and Degenerative Scoliosis” came to my attention as it was reported In the Wall street Journal. I chased the actual study down to  an obscure Journal
Global advances in Health and Medicine.
So, it  got some people to perform the side plank
“Results: The mean self-reported practice of the side plank was 1.5 minutes per day, 6.1 days per week, for a mean follow-up period of 6.8 months. Among all patients, a significant improvement in the Cobb angle of the primary scoliotic curve of 32.0% was found. Among 19 compliant patients, the mean improvement rose to 40.9%. Improvements did not differ significantly among adolescent idiopathic and degenerative subtypes (49.6% and 38.4%, respectively).
Conclusions: Asymmetrically strengthening the convex side of the primary curve with daily practice of the side plank pose held for as long as possible for an average of 6.8 months significantly reduced the angle of primary scoliotic curves. These results warrant further testing”
My own take on this  is that  no harm resulted from this experiment, and it makes sense to test  strengthening both sides. The core  and torso needs to be braced: lets do it all! I should say the self reporting , does not make this the best evidence ever, but , interesting . The side plank is used by Stuart McGill in the treatment of back pain. It seems safe, if monitored, to use and test.
We will see how my client responds