Hi Emily. No not the end of the road at all.
There are many reasons why a test may show results lower than you might expect, especially in young children. As a starting point, this is a long article from the Hoagies page which explains some of the reasons. Scroll down the page to Types of Tests and Intelligence tests. Olsat is a group test so subject to all the possible issues of any group test situation, distractions from noise or other people, not hearing the instructions, thinking outside the box when answering the questions. These are things that can be adjusted for or noted in an individual testing situation.
You will see the Hoagies article comments on learning disabilities. That can be a whole range of things from hearing and eyesight to inattention, poor motor coordination etc etc. An individual tester would note clues for these things.
Having said all that, you have a bright child. If there are reasons to think they might be gifted then an individual assessment could be worth pursuing. Testing is only really valuable if there is a question you need answered in regard to your child's learning or to access services they need, including gifted or learning disabled services. Schools may do the testing or it can be done privately but at a cost, sometimes a significant one. A combination of intelligence and achievement testing may be needed or other test batteries if a learning disability is being examined which add to the cost.
http://www.hoagiesgifted.org/tests_tell_us.htm
