School Food Modernization Act - Directs the Secretary of Agriculture (USDA) to issue loan guarantees to local educational agencies (LEAs) participating in the school lunch program, tribal organizations, or consortia of such entities to finance the construction, remodeling, or expansion of infrastructure or the purchase of durable equipment that will facilitate their provision of healthy meals through the school breakfast and lunch programs. Requires the Secretary to give a preference to applicants that, compared with other applicants, demonstrate a substantial or disproportionate need for food service infrastructure or durable equipment. Prohibits a loan guarantee from covering more than 90% of a loan's principal.

Amends the Child Nutrition Act of 1966 to direct the Secretary to award competitive grants to assist LEAs participating in the school lunch program, tribal organizations, or consortia of such entities in purchasing the durable equipment and infrastructure they need to serve healthier meals and improve food safety. Gives grant priority to applicants that serve a high percentage of students eligible for free or reduced price meals under the school lunch program.

Directs the Secretary to award competitive matching grants to experienced third-party training institutions to provide school food service personnel with the training and technical assistance they need to meet updated school lunch program nutrition standards.