My child has a high IQ (120 or so) and specific learning disabilities in reading, writing, and math. He fits under the general brain wiring type of classic dyslexia.
His K and 1st grade teachers flagged him for testing because of the discrepancy between his obvious smarts and tremendous difficulty learning to read.
He has had psycho-educational testing every 3-5 years to update his accommodation and learning plan. He is in high school now, and we'll be doing probably his last one this fall, to identify what is needed for SAT/ACT and any accommodations in college.
If school is recommending the testing I'd advice you to get it if you can, OP. It helps to know what problem, exactly, you are dealing with. Your kid is going to be the same kid, with the same strengths and weaknesses, after the test - you'll just understand their needs better. At least that was the case for us. Good luck!