I think EPs tend to use either WISC-IV or BAS, so there are basically these two tests.
Panels vary, I'm afraid, but it's very probable that at least one member of the panel will have some understanding of EP reports.
I agree that you don't want to have to spend time explaining what the report means.
A possible approach is to attach as an appendix to your submission an A4 sheet summarising what WISC-IV entails. For example, from https://en.wikipedia.org/wiki/Wechsler_Intelligence_Scale_for_Children
A total of five composite scores can be derived with the WISC–IV. The WISC-IV generates a Full Scale IQ (FSIQ) which represents overall cognitive ability, the four other composite scores are Verbal Comprehension index (VCI), Perceptual Reasoning Index (PRI), Processing Speed Index (PSI) and Working Memory Index (WMI).
Each of the ten core subtests is given equal weighting towards full scale IQ. There are three subtests for both VCI and PRI, thus they are given 30% weighting each; in addition, PSI and WMI are given weighting for their two subtests each. The WISC-IV also produces seven process scores on three subtests: block design, cancellation and digit span. These scores are intended to provide more detailed information on cognitive abilities that contribute to performance on the subtest. These scores do not contribute to the composite scores.
The VCI's subtests are as follows:
Vocabulary - examinee is asked to define a provided word.
Similarities - asking how two words are alike/similar.
Comprehension - questions about social situations or common concepts.
Information (supplemental) - general knowledge questions.
Word reasoning (supplemental)- a task involving clues that lead to a specific word, each clue adds more information about the object/word/concept.
The Verbal Comprehension Index is an overall measure of verbal concept formation (the child's ability to verbally reason) and is influenced by knowledge learned from the environment.
The PRI's subtests are as follows:
Block Design - children put together red-and-white blocks in a pattern according to a displayed model. This is timed, and some of the more difficult puzzles award bonuses for speed.
Picture Concepts - children are provided with a series of pictures presented in rows (either two or three rows) and asked to determine which pictures go together, one from each row.
Matrix Reasoning - children are shown an array of pictures with one missing square, and select the picture that fits the array from five options.
Picture Completion (supplemental) - children are shown artwork of common objects with a missing part, and asked to identify the missing part by pointing and/or naming.
The WMI's (formerly known as Freedom from Distractibility Index) subtests are as follows:
Digit Span - children are orally given sequences of numbers and asked to repeat them, either as heard and in reverse order.
Letter-Number Sequencing - children are provided a series of numbers and letters and asked to provide them back to the examiner in a predetermined order.
Arithmetic (supplemental) - orally administered arithmetic questions. Timed.
The PSI's subtests are as follows:
Coding - children under 8 mark rows of shapes with different lines according to a code, children over 8 transcribe a digit-symbol code. The task is time-limited with bonuses for speed.
Symbol Search - children are given rows of symbols and target symbols, and asked to mark whether or not the target symbols appear in each row.
Cancellation (supplemental)- children scan random and structured arrangements of pictures and marks specific target pictures within a limited amount of time.
Or, from http://www.brainy-child.com/expert/WISC_IV.shtml
(where the four main indexes are nicely set out in boxes):-
The following shows the four main indexes of the WISC-IV and what they measure
Verbal Comprehension Index (VCI)
Measure: Verbal concept formation.
It assesses children's ability to listen to a question, draw upon learned information from both formal and informal education, reason through an answer, and express their thoughts aloud. It can tap preferences for verbal information, a difficulty with novel and unexpected situations, or a desire for more time to process information rather than decide "on the spot."
Note: This index is a good predictor of readiness for school and achievement orientation, but can be influenced by background, education, and cultural opportunities.
Perceptual Reasoning Index (PRI)
Measure: Non-verbal and fluid reasoning.
It assesses children's ability to examine a problem, draw upon visual-motor and visual-spatial skills, organize their thoughts, create solutions, and then test them. It can also tap preferences for visual information, comfort with novel and unexpected situations, or a preference to learn by doing.
Working Memory Index (WMI)
Measure: Working memory.
It assesses children's ability to memorize new information, hold it in short-term memory, concentrate, and manipulate that information to produce some result or reasoning processes. It is important in higher-order thinking, learning, and achievement. It can tap concentration, planning ability, cognitive flexibility, and sequencing skill, but is sensitive to anxiety too. It is an important component of learning and achievement, and ability to self-monitor.
Processing Speed Index (PSI)
Measure: Processing speed.
It assesses children's abilities to focus attention and quickly scan, discriminate between, and sequentially order visual information. It requires persistence and planning ability, but is sensitive to motivation, difficulty working under a time pressure, and motor coordination too. Cultural factors seem to have little impact on it. It is related to reading performance and development too. It is related to Working Memory in that increased processing speed can decrease the load placed on working memory, while decreased processing speed can impair the effectiveness of working memory.
Even experienced panel members may not be familiar with GAI, so you may need to explain that it exists to provide a summary score that is less sensitive to the influence of working memory and processing speed. (I suspect that in your child's case the EP feels that WMI or PSI might be distorting the FSIQ, and that the GAI is a better reflection of overall ability.)