Correct option is A
When a school allows a gifted child to skip grades and move directly to a higher grade, it is using the approach of acceleration. Acceleration involves advancing students to higher grades or classes that match their advanced intellectual abilities, providing them with academic content that is appropriate for their level of understanding and learning pace. This differs from enrichment, encouragement, or synthesis, as it specifically involves moving students through the educational system at a pace faster than typical. Therefore, acceleration is the approach used in this scenario.