In the ESSA (Every Student Succeeds Act) the following is found: “school districts must inform parents of their rights under State law or local policy to opt their children out of any assessments mandated by the Act, by the state, or by the local school district”. That provision is found in two places. The first requires each school district (local educational agency in federal parlance) to notify parents that they may request and will timely receive information about state and local opt-out policies:

Section 1111(e)(2), which reads:

‘‘(e) PARENTS RIGHT-TO-KNOW.—
‘‘(2) TESTING TRANSPARENCY.—
‘‘(A) IN GENERAL.—At the beginning of each school year, a local educational agency that receives funds under this part shall notify the parents of each student attending any school receiving funds under this part that the parents may request, and the local educational agency will provide the parents on request (and in a timely manner), information regarding any State or local educational agency policy regarding student participation in any assessments mandated by section 1111(b)(2) and by the State or local educational agency, which shall include a policy, procedure, or parental right to opt the child out of such assessment, where applicable.
‘‘(B) ADDITIONAL INFORMATION.—Subject to subparagraph (C), each local educational agency that receives funds under this part shall make widely available through public means (including by posting in a clear and easily accessible manner on the local educational agency’s website and, where practicable, on the website of each school served by the local educational agency) for each grade served by the local educational agency, information on each assessment required by the State to comply with section 1111, other assessments required by the State, and where such information is available and feasible to report, assessments required districtwide by the local educational agency, including—
‘‘(i) the subject matter assessed;
‘‘(ii) the purpose for which the assessment is designed and used;
‘‘(iii) the source of the requirement for the assessment; and
‘‘(iv) where such information is available—
‘‘(I) the amount of time students will spend taking the assessment, and the schedule for the assessment; and
‘‘(II) the time and format for disseminating results.
‘‘(C) LOCAL EDUCATIONAL AGENCY THAT DOES NOT OPERATE A WEBSITE.—In the case of a local educational agency that does not operate a website, such local educational agency shall determine how to make the information described in subparagraph (A) widely available, such as through distribution of that information to the media, through public agencies, or directly to parents.

The second is in Section 1111(b)(2)(K)m which ensures that State or local laws allowing parents to opt their children out of assessments cannot be overruled by the U.S. Department of Education. Section 1111(b)(2)(K) reads:

‘‘(2) ACADEMIC ASSESSMENTS.—
‘‘(K) RULE OF CONSTRUCTION ON PARENT RIGHTS.—
Nothing in this paragraph shall be construed as preempting a State or local law regarding the decision of a parent to not have the parent’s child participate in the academic assessments under this paragraph.

The ESSA requirement for schools to meet the 95% Participation Rate under ESSA is found at:

Sec. 1111
‘‘(c) STATEWIDE ACCOUNTABILITY SYSTEM.—
‘‘(4) DESCRIPTION OF SYSTEM.—
‘‘(E) ANNUAL MEASUREMENT OF ACHIEVEMENT.—
Annually measure the achievement of not less than 95 percent of all students, and 95 percent of all students in each subgroup of students, who are enrolled in public schools on the assessments described under subsection (b)(2)(v)(I).
‘‘(IV) the weight of any measure or indicator used to identify or meaningfully differentiate schools, under this part;
‘‘(V) the specific methodology used by States to meaningfully differentiate or identify schools under this part;

HOWEVER, ESSA also includes this, which means that meeting the 95% requirement is no longer a pass/fail indicator all on its own if states don’t want it to be. A state could, for example, give a weight of 0.1% to participation rate in evaluating schools and the Department cannot make them do otherwise:

Sec. 1111
‘‘(e) PROHIBITION.—
‘‘(1) IN GENERAL.—Nothing in this Act shall be construed to authorize or permit the Secretary—
‘‘(B) as a condition of approval of the State plan, or revisions or amendments to, the State plan, or approval of a waiver request submitted under section 8401, to—
‘‘(iii) prescribe—
‘‘(III) indicators that States use within the State accountability system under this section, including any requirement to measure student growth, or, if a State chooses to measure student growth, the specific metrics used to measure such growth under this part;
‘‘(IV) the weight of any measure or indicator used to identify or meaningfully differentiate schools, under this part;
‘‘(V) the specific methodology used by States to meaningfully differentiate or identify schools under this part;
‘‘(XI) the way in which the State factors the requirement under subsection (c)(4)(E)(i) [the 95% participation rate; see above] into the statewide accountability system under this section; or
‘‘(C) to issue new non-regulatory guidance that—
‘‘(i) in seeking to provide explanation of requirements under this section for State or local educational agencies, either in response to requests for information or in anticipation of such requests, provides a strictly limited or exhaustive list to illustrate successful implementation of provisions under this section; or
‘‘(ii) purports to be legally binding;