This article investigates the so-called isomorphism effect (Musolino 1998; Musolino, Crain & Thornton 2000) in the comprehension of scopally ambiguous sentences containing negation and floating quantifiers. Given that floating quantifiers can appear in up to three surface positions relative to negation, I propose that they provide us with the ideal methodological tool to test for scope ambiguity resolution while holding constant various factors, including: (i) the associated noun phrase, and thereby the relevant thematic roles in the test stories; (ii) the syntactic position of the associated noun phrase, and thereby the relevant interpretive mechanism for achieving either a wide or narrow scope construal; (iii) the discourse contexts in which the test sentences are presented. Using a truth value judgment task, I show that both 4-year-olds and adults display isomorphic preferences in their interpretation of ambiguous sentences containing the floating quantifier all, no matter its surface position. In the case of both, children and adults display a preference for isomorphism only when both precedes negation. Crucially, for both quantifiers, children and adults display the same interpretive preferences, lending further support to the general view that children and adults do not differ in their grammatical representations of such scopally ambiguous sentences (Musolino & Lidz 2003, 2006; Gualmini 2004; Conroy, Lidz & Musolino 2009).