Since UNESCO's Salamanca Declaration in 1994, inclusive education has progressively attracted attention in international debates around education policy. While some evidence exists on the positive impact that inclusive education reforms can have on the academic and personal outcomes of diverse students -- and in particular of students with special education needs -- limited information is available on the economic sustainability of such reforms. Starting from the literature on the correlations between education and individuals' life outcomes, this paper reviews the existing evidence on the potential benefits and costs of inclusive education reforms. Specifically, the paper discusses the evidence on the shortcomings of current education settings for diverse groups of students -- with specific sections on students with special education needs; immigrant and refugee students; ethnic groups, national minorities and Indigenous peoples; gifted students; female and male students; and LGBTQI+ (which stands for 'lesbian, gay, bisexual, transgender, queer and intersex') students. It highlights the individual and societal costs deriving from the low academic, social and emotional outcomes of these students and the socio-economic costs these yield for societies. Where possible, the paper also presents evidence on the effects of inclusive education reforms on diverse student groups.