Evidence on inequality of opportunity in terms of educational achievement (IOpE) is still scarce and has not yet explored the relevance of different contributors and channels. Using the latest microdata from the 2018 Programme for International Student Assessment, we find that IOpE accounts, on average, for 32% of total educational inequality in Western Europe, with substantial variation across countries. Differences in households’ cultural environment and in parental occupation are the most important contributors, with school’s characteristics being also relevant in Central Europe. We then estimate for the first time the role of channelling variables in translating differences in circumstances into different educational achievement.In most countries, students’ educational and occupational expectations, their reading habits and skills, and the repetition of previous courses are the most influential channels. These findings provide policymakers with key insights to design educational interventions to effectively increase educational and, ultimately, social opportunities across European countries.