Admission-wise, Earlham has marginally higher test score ranges, but Kalamazoo has slightly higher HS GPA and class rank profiles. That should suggest a slightly higher success rate at Kalamazoo (HS record tends to be more predictive than test scores of college academic success), but not as large as mentioned above. Both claim to meet 94-95% of need, but NPC runs suggest that both will be unaffordable for students from low income (full Pell) families (though Kalamazoo looks worse). However, both appear to have a significant merit component in their financial aid (nearly all students at both get some grants or scholarships), so they could be more affordable for students from low income families who earn whatever merit or semi-merit based aid they give.
It looks like Earlham enrolls a significantly higher percentage of Pell grant frosh than Kalamazoo (36% versus 27%). But both have similar percentage of Pell grant overall undergraduates (27% versus 24%), suggesting that Earlham has difficulty retaining Pell grant students in particular.
Unlike many other cases, the difference in graduation rates between Earlham and Kalamazoo is not significantly explained by the usual factors (incoming student academic profile, financial aid, incoming student financial profile) that explain much of the difference in graduation rates generally.