I think we are mixing up Weymouth schools
1. Weymouth Secondary School Cadets are listed in 1919 Army List. The school was formed in 1913.
2. Weymouth College had the OTC which was formed in 1914 (I have found a reference to a Weymouth College cadet corps being disbanded in 1902)
Separate units but one a cadet corps and one a Junior Division OTC.
I have seen the photo attributed to the OTC but I too think it is the cadet corps as you suggest.
The cadet corps were affiliated to the 4th TF Bn Dorsetshires but so were Sherborne and they had their own school cap badge. I have never seen a photo of a cadet to identify what cap badge they wore but you are right that the school badge was a lion so with the photo as evidence that's a new CC badge added to the list - possibly officers only but still a new one for my list. The acdte corps was still going in 1927
http://westlulworth.org.uk/news_1927.html
Many thanks