The CTS (I & D) Exam Guides
Exclusively from McGraw-Hill and AVIXA, the series of exam guide books cover exam objectives relative to each respective certification (CTS, CTS-D, CTS-I) with detailed coverage of the technical topics common to each job role.
Find more info here CTS Exam Guides (avixa.org)
Neither AVIXA nor McGraw-Hill warrants that use of these publications will ensure passing any exam. Practice exam questions were not subject to the same item development process as questions on the actual exam and may or may not reflect the actual exam experience.
Remember, though, you are not required to purchase any courses or resources to prepare for the exam.