Document data: Ministry of Education and Science (MES). Link: https://www.izm.gov.lv/lv/media/4093/download , see “pa plūsmām” (by streams).
Publisher’s notes: education fully in Latvian in 1998/99 was available in 873 schools, in 2019/20 in 605 (a fall of 31 %). Education partly in Russian in 1998/99 was available in 340 schools, in 2019/20 in 142 (a fall of 58 %).
It should be noted that the sole Belarusian school is a [public] basic school only. According to Wikipedia, it was founded in 1994. The [private] German primary school has only appeared in 2016, and is considered to be more oriented to expatriates than to the historical German minority.
There exist two Jewish secondary schools (a public one and a private one), one public Lithuanian secondary school and one public Estonian basic school (downgraded from a secondary one), all in Riga. They do not appear separately in the MES statistics. Judging by the city education portal iksd.riga.lv , the Lithuanian and Estonian schools are not implementing a minority education programme, so in the MES statistics they probably are classified under “Latvian” ones. The Jewish schools are supposedly classified by MES by language as “dual stream”.
Relevant international recommendations
201. [..] ensure continued availability of teaching and learning in languages of national minorities throughout the country with a view to meeting the existing demand
Advisory Committee on the Framework Convention for the Protection of National Minorities. Opinion ACFC/OP/III(2018)001; adopted 23.02.2018, published 15.10.2018 Link: https://rm.coe.int/revised-version-of-the-english-language-version-of-the-opinion/1680901e79 [text highlighted among “Issues for immediate action”]
90. [..] Therefore, in order to ensure that the right to minority language instruction is implemented adequately throughout Latvia, it is preferable that the legislation impose a clear obligation for a presence of sufficient state schools offering a minority education programme whenever there is enough demand for it.
Venice Commission. CDL-AD(2020)012; Opinion No. 975/2020. 18.06.2020 Link: https://www.venice.coe.int/webforms/documents/?pdf=CDL-AD(2020)012-e