There is a huge range of art classes in Perth, available for all ages and as an after-school activity. Here are a few websites you can check out, based on what you want to learn.
Art (General):
http://atwellarts.weebly.com/atwell-arts-centre.html --> Check Out Our Art Classes --> *select your level* http://canningartsgroup.vpweb.com.au/children-s
http://canningartsgroup.vpweb.com.au/adults
http://artclassesperth.com
http://www.perthartschool.com
https://www.fac.org.au
Pottery: http://canningartsgroup.vpweb.com.au/children-s
http://canningartsgroup.vpweb.com.au/adults
http://www.grahamhay.com.au/classes.html#.V5NTH4RhPpA
http://perthartclasses.com
Painting:
http://www.maliniparker.com --> Art Classes --> *select your level*
http://karenfrankelart.com ---> Classes --> *select your level*
http://www.janavodesil.com/classes-workshops/
http://renatawrightart.net/watercolour-painting-classes/
http://www.janavodesil.com/classes-workshops/
Other:
http://perthartclasses.com (Sewing)
