The drop is not uniform; see Table I.2.6 (2022 -> 2025). Focusing on math:

Stable, above OECD average: Taiwan, Macao, Korea, Estonia, United Kingdom, Poland, Lithuania, Italy, New Zealand

Stable, around or below OECD average: United States, Slovakia, Greece, Croatia, Qatar, Montenegro, Mongolia, Mexico, Brunei

Dropping, previously above OECD average: Singapore, Japan, Hong Kong, Switzerland, Canada, Netherlands, Ireland, Australia, Belgium, Austria, Denmark, Finland, Germany, Sweden, Slovenia, Latvia, Portugal, Norway, Spain, France, Hungary

Dropping, around or below OECD average: Iceland, Israel, Malta, Serbia, Chile, Bulgaria, Kazakhstan, Argentina, Malaysia, Romania, Peru, Ukraine, North Macedonia

Improving, all below OECD average: Türkiye, Thailand, UAE, Philippines, Jordan, Georgia, Cambodia