Displaying a test score within ranges of a category

Hi Everyone,

Tableau newbie here trying (and failing!) to do something that seems like it should be easy enough to do. I want to derive 3 test score ranges from a categorical variable and then use those to show a stacked bar graph with each range. Example, say I have below, average, and above average IQ as a categorical variable. I want to generate ranges from all test scores to get to one bar graph that displays these ranges, e.g. if score could be 0-30, then 30 to bottom of stdev from median of "Above Average" would be the top range, bottom of stdev of "Average" would be second range, and anything below would be the third range. Then I would want to be able to display individual test scores as circle on top of the bar chart of ranges. I sketched out what I am thinking about. I'm not sure if this is clear at all but any help would be appreciated, even just pointing to some resources online if they exist. Thanks!