No. "Grades" is only one component of many that must be considered for eligiblity of an IEP.
And yes, when a child is having behavioral problems, it adversely impacts his/her education and the other students' as well.
Although it appears to be a reoccurring misinterpretation of IDEA by some educators, the regs are clear. From
https://web.archive.org/web/2008051...0/edocket.access.gpo.gov/2006/pdf/06-6656.pdf
"FAPE Requirements
Section 300.101(c) has been revised
to clarify that a free appropriate public
education (FAPE) must be available to
any individual child with a disability
who needs special education and
related services, even though the child
has not failed or been retained in a
course, and is advancing from grade to
grade....
...Comment: Some commenters
expressed concern that children with
disabilities have to fail or be retained in
a grade or course in order to be
considered eligible for special education
and related services.
Discussion: Section 300.101(c)
provides that a child is eligible to
receive special education and related
services even though the child is
advancing from grade to grade. Further,
it is implicit from paragraph (c) of this
section that a child should not have to
fail a course or be retained in a grade in
order to be considered for special
education and related services. A public
agency must provide a child with a
disability special education and related
services to enable him or her to progress
in the general curriculum, thus making
clear that a child is not ineligible to
receive special education and related
services just because the child is, with
the support of those individually
designed services, progressing in the
general curriculum from grade-to-grade
or failing a course or grade. The group
determining the eligibility of a child for
special education and related services
must make an individual determination
as to whether, notwithstanding the
childs progress in a course or grade, he
or she needs or continues to need
special education and related services.
However, to provide additional clarity
we will revise paragraph (c)(1) of this
section to explicitly state that children
do not have to fail or be retained in a
course or grade in order to be
considered eligible for special education
and related services.
Changes: Section 300.101(c)(1) has
been revised to provide that children do
not have to fail or be retained in a
course or grade in order to be
considered eligible for special education
and related services.
....We also recognize, though, that as a
matter of practice, it makes a great deal
of sense to attend to behavior of
children with disabilities that is
interfering with their education or that
of others, so that the behavior can be
addressed, even when that behavior will
not result in a change in placement. In
fact, the Act emphasizes a proactive
approach to behaviors that interfere
with learning by requiring that, for
children with disabilities whose
behavior impedes their learning or that
of others, the IEP Team consider, as
appropriate, and address in the childs
IEP, the use of positive behavioral
interventions, and other strategies to
address the behavior. (See section
614(d)(3)(B)(i) of the Act). This
provision should ensure that children
who need behavior intervention plans to
succeed in school receive them. For
these reasons, we decline to make the
changes suggested."